Soil Organic Carbon Dynamics and Carbon Sequestration Under Conservation Tillage in Tropical Vertisols

Abstract

Soils, especially managed agricultural soils, have the potential to sequester carbon (C) and contribute to the mitigation of GHGs emissions. Increasing the amount of organic matter addition to soils may not only mitigate GHG emissions, but also benefit agricultural productivity through improvements in soil health and environmental quality. One potential method for increasing the amount of C held in agricultural soil is through conversion of conventional tillage practices to conservation tillage practices that reduce tillage and retain crop residues. Vertisols in India occupy 8.1% of the total geographical area of the country and are generally low in organic carbon content, but these soils have great potential to increase the soil organic carbon (SOC) level. Improvement in SOC content in these soils through traditional/conventional soil management practices is very difficult, as it has already attained the equilibrium level. One of the most attainable pathways to improve and sequester SOC content in this soil is through either regular addition of organic manures such as farmyard manure, compost or crop residues or by switching traditional tillage practices to no-tillage or other forms of conservation tillage. Several long- and short-term field studies on Vertisols reported that management strategies, such as no-tillage (NT) and reduced tillage (RT) with residue retention, played a significant role in increasing SOC concentration and favouring aggregate stability. Adoption of conservation tillage practices resulted in an improvement of surface soil aggregation and an increase in the proportion of macroaggregates compared to conventional tillage. Conservation tillage increases the percentage of carbon-rich macroaggregates in the soil particularly in the surface layers, resulting in sequestration of more carbon into soil stabilized through physical protection. More aggregate-C in large and small macroaggregates favoured better aggregation under conservation tillage than that under conventional tillage, which suggested that macroaggregates are sensitive to changes in the soil microbial community associated with short-term conservation management practices. Conservation tillage also resulted in stratification of SOC and available nutrient levels in soil. Conservation tillage in tropical Vertisols could be a useful technology to partially mitigate the deleterious effect of climate change through sequestration of carbon into the soil and reduction of greenhouse gas emission from agricultural activities to atmosphere. It also improves soil health, its resilience to extraneous stresses and the sustainability of agricultural production system.